Significance of Meiosis

Meiosis carries a significance out of all proportion to the simple fact that it halves the chromosome number. It is precisely because it halves that number that sexually reproducing species are able to keep their chromosome number steady from one generation to the next, and it is the reshuffling that meiosis brings about that supplies the raw variation on which evolution works.

Keeping the chromosome number constant

Meiosis is the mechanism through which each species preserves its own particular chromosome number across the generations in organisms that reproduce sexually. This may seem contradictory at first, because the process itself, taken on its own, actually cuts the chromosome number in half. The resolution lies in the life cycle as a whole:

• Meiosis reduces the chromosome number by half while producing the gametes, so each gamete carries the haploid (n) set.
• At fertilisation, two such gametes fuse, and the fusion restores the chromosome number to the full diploid (2n) value characteristic of the parent.

Without this halving before fertilisation, the chromosome number would double every generation, so meiosis is what allows the number to remain fixed across generations.

Generating genetic variation …